A PMR write head typically has a main pole with a small surface area at an air bearing surface (ABS), and coils that conduct a current and generate a magnetic flux in the main pole such that the magnetic flux exits through a write pole tip and enters a magnetic medium (disk) adjacent to the ABS. Magnetic flux is used to write a selected number of bits in the magnetic medium and typically returns to the main pole through two pathways including a trailing loop and a leading loop. The trailing loop generally has a trailing shield structure separated from the main pole by a write gap, and the leading loop includes the leading shield that is separated from the main pole by a leading gap. Side shields are relied on to enhance the cross-track field gradient.
Shingled magnetic recording (SMR) is a form of PMR and has been proposed for future high density magnetic recording by R. Wood et al. in “The Feasibility of Magnetic Recording at 10 Terabits Per Square Inch on Conventional Media”, IEEE Trans. Magn., Vol. 45, pp. 917-923 (2009). In this scheme, tracks are written in a sequential manner from an inner diameter (ID) to an outer diameter (OD), from OD to ID, or from OD and ID towards a middle diameter (MD) in a radial region of a disk in a hard disk drive (HDD). In other words, a first track is partially overwritten on one side when a second track adjacent to the first track is written, and subsequently a third track is written that partially overwrites the second track, and so forth. Track widths are defined by the squeeze position or amount of overwrite on the next track rather than by the write pole width as is the case in today's hard drives.
One of the main advantages of shingled writing is that write pole width no longer needs to scale with the written track width. Thus, the opportunity for improved writability and higher device yield is not restricted by using pole width as a critical dimension to be tightly controlled. Secondly, adjacent track erasure (ATE) becomes less of an issue because tracks are written sequentially in a cross-track dimension and only experience a one time squeeze from the next track.
In today's PMR writer design, the geometries and dimensions of the main pole and side shields are key factors for both overwrite and dBER (delta bit error rate) performance in hard disk drives (HDD). In a fully coupled shield (FCS) where the trailing shield, leading shield, and side shields completely surround the main pole at the ABS, the side shields are first plated on the leading shield, then a conformal non-magnetic material is deposited to form a leading gap and side gaps on the exposed surface of leading shield, and sidewalls of the side shields, respectively. Next, the main pole is plated on the leading gap and side gaps. As a result, the main pole shape proximate to the ABS is mainly defined by the shape of adjacent portions of the side shields. There is always flux leakage between the side shields and main pole due to thin side gaps in current writer designs. A write head that can deliver or pack higher bits per inch (BPI) and higher tracks per inch (TPI) is essential to the area density improvement. If writeability can be sustained, the main pole size must shrink, and a thinner write gap at the main pole trailing (top) surface and a narrower side gap adjoining the main pole sides in the cross-track direction are preferred for better track field gradient (Hy_grad, BPI) and cross-track field gradient (Hy_grad_x, TPI), respectively. However, with extremely narrow magnetic spacing between the main pole and surrounding shields, internal flux shunting becomes severe and is the major factor for a dramatic decrease in OW and writability degradation.
Therefore, a new side shield and main pole design is needed to minimize internal flux shunting in order to provide improved writability while maintaining high TPI capability for advanced writers with thin side gaps.